Semiconductor device-fabricating processes, for example, use various type of cleaning apparatuses for cleaning a semiconductor wafer (hereinafter, referred to simply as “wafer”). For example, a cleaning process for cleaning a wafer having a surface coated with a polysilicon film before forming a tungsten silicide film or the like on the polysilicon film includes a step of immersing the wafer in a chemical, such as a dilute hydrofluoric acid solution (DHF solution), contained in a processing tank, a step of rinsing the wafer with pure water, and a step of drying the wafer by spraying isopropyl alcohol (IPA) or steam on the wafer.
A known cleaning system for carrying out such a cleaning process disclosed, for example, in Patent document 1 includes a processing tank for carrying out a chemical process, and a drying unit for carrying out a drying process disposed above the processing tank. A top cover covering an open upper end of a vessel is opened, a wafer is carried through the open upper end into the vessel, and the wafer is moved down through a drying unit placed in the vessel into a processing tank. Then, the wafer is subjected to a chemical process and a rinsing process, the wafer is raised into the drying unit, and IPA vapor is sprayed on the wafer for drying while the wafer is being raised through the drying unit. Subsequently, the vessel is purged by using nitrogen gas, and then the top cover is opened to carry out the wafer from the vessel.
Patent document 1: Jpn. Pat. No. 3126858
A conventional substrate-processing system has a difficulty in controlling air currents in the drying unit. Consequently, a chemical atmosphere produced in the processing tank flows upward into the drying unit and remains on the inside surface of the vessel. Since the IPA vapor tends to adhere to the inside surface of the vessel, the IPA vapor cannot be efficiently sprayed on the wafer. Consequently, a large quantity of the IPA vapor is consumed and the IPA vapor stays on the inside surface of the vessel. The chemical atmosphere and the IPA vapor remaining on the surface of the wafer form a water mark on the surface of the wafer, obstruct the formation of a normal film on the surface of the thus cleaned wafer and cause problems in the electrical characteristic of semiconductor devices formed by processing the wafer.